This invention relates to pneumatic controls for ship propulsion systems, and more specifically to an improved system for transferring control between several control stations.
A common form of marine propulsion system employs ahead and astern air actuated clutches for connecting the prime mover to a reversing reduction gear unit for each propeller. The air actuated clutches are engaged by inflation and the degree of clutch engagement can be controlled by controlling the amount of inflation. A pneumatic control system is normally provided for controlling the amount of inflation and this control system also typically provides control for an engine speed governor which determines the engine speed. A single throttle lever apparatus can be provided for controlling both the clutch engagement and engine speed by movement of the lever in an ahead or astern direction from neutral. An example of such a control for a ship's propulsion system is found in my earlier U.S. Pat. No. 3,727,737, issued Apr. 17, 1973, for "Pressure Modulating System for Reversing Clutches and Throttle Control".
It is common to provide more than one control station. Thus, both engine room and pilot house control stations are typically provided. With larger vessels, visibility from the pilot house may be limited in one or more directions so that it is desirable to locate additional control stations at sites offering a view of a specific area of the ship such as at a winch, the side of the ship, or at a higher position in the pilot house for a better forward view. The several control stations are typically duplicates of each other with each offering full control of the propulsion system.
Transfer systems are in use in marine controls which allow any of the several control stations to operate the vessel. This is normally accomplished by switching the supply of compressed air used in the control, and in clutch inflation, to a specific one of the control stations. Two versions of supply air transfer stations are presently in use. In one, the supply air is directed to the desired station which is then turned on prior to use by the operator. This system places the controls in neutral during each transfer and allows operation only by the specific control station which is selected. The difficulty with this approach is that it does not allow for the maintaining of tension on a towing cable or the maintaining of headway against the current while changing operating stations because the controls are placed in neutral in each transfer.
The second approach in use maintains the speed control signals during the transfer cycle and permits control by any station at any time. The disadvantage of this approach is that it permits transfer to an unattended operating station. If that unattended operating station has been left in some control mode other than neutral, it immediately becomes active and operates the vessel.
I have developed a system for transferring control between remote stations which requires an initial operation at a particular station in order to make that station active so that transfer cannot be made to an unattended station. At the same time, my transfer system maintains a control signal during the period of transfer from one station to another.